Veggie mums are more likely to be lacking in B12 vital for brain development

They found meat-free pregnant mums were almost twice as likely to have a teenager who drank heavily or smoked cigarettes compared with those who ate meat daily.

They were also nearly three times more likely to have a child who smoked cannabis, according to the National Institute on Alcohol Abuse and Alcoholism. The US agency analysed data on 5,109 British kids and their mums.

Researchers say mums that eat little or no meat are often missing out on vitamin B12, with 62 per cent of vegetarians deficient in this nutrient during pregnancy.

Infants whose mums are lacking in B12 – also known as cobalamin – typically have poorer brain development, are more irritable, and exhibit weaker social and mental skills.

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Rather than eating meat, vegetarian mums are advised to have fortified food or take supplements

Study leader Dr Joseph Hibbeln said "vegetarians could eat food fortified with B12, including certain breakfast cereals, or take supplements.

"Reducing meat consumption is often advised but this study identifies low meat consumption in the prenatal period as potentially modifiable risk factor for adolescent substance use."

However, Dr Irene Petersen from University College London advised caution. She said: “There are so many other factors that determine whether a young adult drinks, smokes or takes drugs.